Electrical contact and method of fabrication

ABSTRACT

An improved electrical contact is disclosed including a heat sink layer secured to a substrate and an electrical contact layer secured to a surface of the heat sink layer. The heat sink layer and the contact layer are each of a generally nonuniform crosssection, including respective central portions of differing thicknesses with respect to the peripheries thereof disposed in mating relationship, with the contact layer terminating spaced inwardly from the periphery of the heat sink layer. In fabrication of the electrical contact the heat sink layer is deposited on the substrate and deformed to include a central portion of decreased thickness, while the contact layer is secured to the surface of the heat sink layer and similarly deformed to include a central portion of an increased thickness in mating relationship with the central portion of the heat sink layer and terminating spaced inwardly from the periphery of the heat sink layer.

United States Patent 1191 Dubuc et al.

1451 Apr. 16, 1974 [73] Assignee: Texas Instruments Incorporated,

Dallas, Tex.

[22] Filed: Mar. 27, 1972 [21] Appl. No.: 238,607

Related US. Application Data [62] Division of Ser. No. 112,534, Feb. 4,1971, Pat. No.

[52] US. Cl. 29/630 C, 29/630 R, 72/47 [51] Int. Cl H011 9/00 [58] Fieldof Search 29/624, 626, 630 C, 630 F,

[5 6] References Cited UNITED STATES PATENTS 3,382,575 5/1968 Gannoe29/630 3,191,275 6/1965 Gwyn 29/15555 3,341,943 9/1967 Gwyn 29/6303,488,841 1/1970 Stern 29/630 Primary Examiner-Charles W. LanhamAssistant ExaminerJames R. Duzan Attorney, Agent, or Firm-Harold Levine;John A. Haug; James P. McAndrews [57] ABSTRACT An improved electricalcontact is disclosed including a heat sink layer secured to a substrateand an electrical contact layer secured to a surface of the heat sinklayer. The heat sink layer and the contact layer are each of a generallynonuniform cross-section, including respective central portions ofdiffering thicknesses with respect to the peripheries thereof disposedin mating relationship, with the contact layer terminating spacedinwardly from the periphery of the heat sink layer. In fabrication ofthe electrical contact the heat sink layer is deposited on the substrateand deformed to include a central portion of decreased thickness, whilethe contact layer is secured to the surface of the heat sink layer andsimilarly deformed to include a central portion of an increasedthickness in mating relationship with the central portion of the heatsink layer and terminating spaced inwardly from the periphery of theheat sink layer.

7 Claims, 7 DrawingFigures ELECTRICAL CONTACT AND METHOD OF FABRICATIONThis is a division, of application Ser. No. 112,534, filed Feb. 4, 1971,now US. Pat. No. 3,686,457.

The present invention relates generally to electrical contacts and moreparticularly is directed to improved multilayer electrical contactsincluding a heat sink layer and an electrical contact layer. Varioustypes of electrical contact arrangements have been developed includingnumerous improvements, such as decreased contact resistance, increasedelectrical lifetime, etc. However, as technology has advanced resultingin decreased costs of various elements utilized in electrical systems aswell as increased durability many electrical contact arrangements arestill considered to have a relatively limited lifetime, particularlywhen exposed to continued repetitive operation in the presence ofelectrical arcing, and in certain instances remain quite expensiverelative to the cost of other elements in such systems due to the usageof precious metals in the contact. More particularly, the currentmagnitude or amperage rating of the contact generally determines thesurface area of the contact material, while the thickness of the contactarrangement generally governs the ultimate lifetime of the contact,since continued arcing eventually results in erosion of the contactmaterial to a point at which the base metal or substrate is exposedresulting in eventual contact failure. Generally it is desirable tofabricate the exposed contact area of a relatively good electricalconductor which is resistant to corrosion and has a low contactresistance. Particularly suitable materials in this regard are silver,gold, and other precious metals which, of course, increase the cost ofthe contact. In order to reduce the cost of the contact, while providingsuitable heat dissipation characteristics, in certain instancesmultilayer contact arrangements have been suggested in which a heat sinksuch as a copper layer, is disposed intermediate the precious metalcontact layer and the substrate or base metal. However, such contactsare still relatively expensive and are expendable in that burn-throughof the contact layer eventually occurs, dictating the usage of increasedquantities of expensive precious metal relative to the heat sink layer.Furthermore, ordinarily in fabricating such contacts the expense offabrication is increased in view of the associated wastage of materialduring processing necessitating the implementation of scrap recoveryprocedures in order to recover all or part of the precious metal and/orcopper scrap which is produced.

Accordingly, it is an object of the present invention to provide animproved method for fabricating an electrical contact device in whichthe usage of expensive materials is minimized and the cost offabrication is reduced.

It is another object of the present invention to provide an improvedmethod for fabricating an electrical contact device in whichsubstantially all of the material being processed is utilized toeliminate the necessity for scrap recovery operations.

It is another object of the present invention to provide an improvedelectrical contact device in which the usage of relatively expensivematerial is minimized, while electrical lifetime is maintained at arelatively high level.

It is another object of the present invention to provide an improvedelectrical contact device which is extremely economical to fabricate anddurable in use.

Various additional objects and advantages of the present invention willbecome readily apparent from the following detailed description andaccompanying drawings wherein:

FIG. 1 is a perspective generally diagrammatic view of a preferredmethod for fabricating an electrical contact device in accordance withthe principles of the present invention;

FIG. 2 is a vertical sectional view of one embodiment of an electricalcontact device in accordance with the present invention;

FIG. 3 is a plan view of the device illustrated in FIG.

FIG. 4 is a vertical sectional view of another embodiment of anelectrical contact device in accordance with the present invention;

FIG. 5 is a plan view of the device illustrated in FIG.

FIG. 6 is a vertical sectional view of still another embodiment of anelectrical contact device in accordance with the present invention; and

FIG. 7 is a plan view of the device illustrated in FIG. 6.

Referring generally to the drawings and initially to FIG. 1 wherein amethod of fabricating an electrical contact device in accordance withthe principles of the present invention is illustrated, a continuoussheet of substrate or support material 10 is carried on a roll 12 andadvanced in the direction indicated. As shown, the sheet of substratematerial 10 may have a plurality of spaced pilot or index apertures 14to aid in suitably positioning the material for subsequent processingoperations. A suitably supported roll 16 carrying a coil of a firstpreselected metallic material 18 is provided adjacent the sheet 10 and,as shown, is adapted to feed the material 18 toward the surface of thesheet 10 where a first securing means 20, such as a suitable weldingapparatus, is provided adjacent the sheet 10 to secure the leading edgeof the material 18 to the sheet. In addition, a suitably supportedcutter means 22 is arranged in alignment with the material 18 foreffecting a separation or cutting operation immediately subsequent tothe securement operation to effect the formation of segments of thematerial 18, defining first bodies 24 of heat sink material, which are,thus, successively deposited at spaced intervals on the surface of thesubstrate sheet 10 as it is continuously advanced. Subsequent tosecurement and separation the body 24 of heat sink material is carriedby the advancing substrate 10 to a position in alignment with a firstcoining means 26 having a suitably shaped die face 27 adapted to deformsubstantially the entire body 24 of heat sink material into apreselected configuration to define a heat sink layer 28 having agenerally nonuniform cross section including a central portion 29 ofdecreased thickness with respect to the periphery thereof. Anothersuitably supported roll 30 which carries a coil of a second preselectedmetallic material 32 is disposed adjacent the output edge of the firstcoining means 26 and, as shown, is adapted to feed the material 32 ontothe exposed surfaces of the respective advancing heat sink layers 28. Asthe material 32 is fed onto the heat sink layers, a second securingmeans 34 such as a suitable welding apparatus, is provided for securingthe leading edge of the material 32 to the surface of the heat sinklayer 28. In addition, a suitably supported cutter means 36 ispositioned in alignment with the material 32 for effecting a cutting orseparation operation immediately subsequent to'the securement operationto provide individual segments of a predetermined length of the-material32, defining second bodies 38 of contact material which are, thus,successively secured to the exposed surfaces of the respective heat sinklayers 28 as the sheet 10 is continuously advanced. The advancing sheet10 then carries the heat sink layer 28 andthe second body 38 to aposition in alignment with a second coining device 40 having a suitablyshaped die face 41 adapted to deform substantially the entire secondbody 38 into a preselected configuration defining an exposed contactlayer 42 having a generally nonuniform cross-section including a centralportion of an increased thickness with respect to the periphery thereofand in mating relationship with the central portion 29 of the heat sinklayer 28, while terminating spaced inwardly from the periphery of theheat sink layer, as shown. A suitable separating device 44 is providedadjacent the output end of the coining device 40 and is adapted toeffect a cut through the sheet 10 along the cut line 46 indicated so asto separate the sheet 10 carrying the spaced respective heat sink andcontact layers into individual portions to define completed units 48.

The substrate material lcarried on the roll 12 preferably comprises arelatively thin sheet of a suitable metallic material. In this regardthe sheet is selected with regard to properties desirable in accordancewith the ultimate environment and application of the contact 48. Forexample, if increased structural strength is desired thin coiled sheetsof various types of low carbon steels may be suitable such as thatcommonly identified as SAE (Society of Automotive Engineers) No. 1010low carbon steel which comprises by weight approximately between 0.08 to0.13 percent carbon, 0.30 to 0.60 percent manganese, 0.040 percent(max.) phosphorous, 0.050 percent (max.) sulphur and the balance iron.Similarly, in certain other instances suitable thin coiled sheets ofbrass or bronze may be utilized, while in other instances thin coiledsheets of phosphor bronze, various monel metals, etc. may be utilized.In the illustrated embodiment the sheet is utilized primarily as acarrier for the heat sink and contact layers and is relatively thin,varying in thickness between approximately 0.008 to 0.070 inch, althoughother thicknesses may be appropriate in certain instances.

The roll 16 of material 18 preferably comprisesa suitably supported rollof a coiled rod-like member or wire of material having a high thermalconductivity, such as substantially pure copper wire. Copper wire isparticularly advantageous in this regard in view of its readyavailability, low cost, and ease of processing, in this form. The copperwire 18 preferably has a circular cross-section for reasons of economyalthough other cross-sectional configurations may be utilized ifdesired. The copper wire 18 has a preselected diameter such that thebodies 24 formed therefrom are of a sufficient size to permit formationof the heat sink layer 28 in the desired configuration. In theillustrated embodiment the copper wire 18 may have a diameter'of betweenapproximately 0.062 to 0.250 inch, although, if desired, other sizedwire may be utilized. The welding means 20 may comprise any one ofavariety of conventional welding apparatus, although in view of thedifficulty in welding copper due to its high thermal conductivity it isgenerally desirable to utilize a suitable point welding apparatus whichis not shown in detail, since such apparatus is conventionallyavailable. The first coining or deforming means 26 which is disposedadja cent the output edge of the welding means 20 is suitably supportedand may be operated electrically, hydraulically or in other conventionalways, and is arranged to deform substantially the entire body 18 to formthe heat sink layer 28 without any material loss, obviating thenecessity for subsequent scrap recovery operations. ln this connectionthe die face 27 may be shaped to deform the heat sink layer 22 toinclude the generally centrally located depression 29 for accommodatingthe thicker central portion of the contact layer 42 in matingrelationship therewith. Although in the illustrated embodiment theheatsink layer 28 is shown in a generally circular configuration, otherconfigurations may be readily formed suchas rectangular shaped bodies,elliptically-shaped bodies, etc. an important feature being theinclusion of a generally centrally located depression of reducedthickness with regard to the periphery thereof so as to form a layerhaving a nonuniform cross-section to accommodate an increased thicknessof contact layer material at the central region thereof. In theillustrated embodiment the heat sink layer 28 may be deformed to athickness of between approximately 0.010 to 0.125 inch, while thedepression 29 may be formed to extend smoothly from the peripheryprogressively decreasing in thickness or may be formed as an abrupt slotat the center of the layer. Similarly the depression 29 may extendinwardly from the exposed surface of the layer 28 a predetermineddistance depending upon the ultimate application intended for thecontact system, although preferably the depression region retainsapproximately half the thickness of the layer 28 in order to avoidadversely effecting the heat sink properties of the heat sink layer 28.

As the heat sink layer 28 is advanced in the direction indicated towardthe succeeding station at which the roll 30 is positioned the contactbody 38 is secured to the surface of the heat sink layer 28 generally inalignment with the centrally located depression 29. The contact body 38preferably comprises a preselected metallic material having a relativelyhigh electrical conductivity and low contact resistance, as well as goodcorrosion resistance properties. Preferably the contact body comprises amaterial, such as silver, silver cadmium oxide, gold, palladium,platinum or alloys thereof. The contact body material 32 is preferablyinitially provided in the form of a coiled generally rod-like member,such as a circular wire coiled on the roll 30, as previously explainedin connection with the material 18, but may be provided in otherconfigurations, if desired. In the illustrated embodiment the material32 may have a diameter of between approximately 0.020 to 0.l87 inchdepending upon the relative size of the underlying copper heat sinklayer 28 and the ultimate properties desired for the completed contactunit 48, but is reduced in thickness by approximately 50 percent or lessby the second coining means 40 except for the thicker central regiondefined in the subsequently formed contact layer 42. The second securingmeans 38 may again comprise a suitable point welding apparatus adaptedto rigidly attach the contact body 38 to the heat sink layer 28. Afterseparation of the segment defining the contact body 38 from the coil 30subsequent to the welding operation the heat sink layer 28 with thecontact body 38 secured to its surface is advanced to a position inregistration with the die face 41 of the second coining means 40, asshown, which deforms substantially the entire contact body 38 into theconfiguration defining the contact layer 42 without producing any excessmaterial, thereby obviating the necessity for any scrap recoveryoperation. The space defined by the depression 29 in the heat sink layer28 is occupied by the thicker central portion of the contact layer.Futhermore, the contact layer 42 is deformed to extend over apredetermined area of the exposed surface of the heat sink layer 28, butterminates at a location spaced inwardly from the peripheral boundary ofthe heat sink layer 28. The deformed contact layer 42, thus defines aconfiguration in which the central region is of an increased thicknesswith regard to the peripheral portions thereof, while its peripheralboundary is spaced inwardly from the periphery of the heat sink layer28. In a preferred embodiment the contact layer 42 may occupy betweenapproximately 50 to 90 percent of the exposed surface area of the heatsink layer, thereby re ducing the usage of the relatively expensivecontact layer material while providing increased quantities of contactmaterial at the critical central region of the contact unit 48 wheresuch material is needed. As may be seen the sheet including the heatsink layer 28 and the contact layer 42 is then advanced to a position inregistration with the separating means 44 which effects a cut along theseparation line 46 to provide the composite completed contact unit 48.Although in the preceding description and accompany drawing the segmentsof heat sink material and contact layer material are sucured to thesubstrate sheet at their respective exposed end edges and hence are in avertical orientation prior to deformation, it should be noted that incertain instances the segments may be disposed on the advancingsubstrate sheet in a horizontal orientation with a portion of the outersurface of the segment being secured in position prior to deformation.

Various embodiments of contact units such as the unit 48 are illustratedand described in detail hereinafter indicative of typical examples ofcontact units in accordance with the present invention which may befabricated utilizing a method such asthat described in detail inconnection with FIG. 1 by varying the shape of the die faces 27, 41 ofthe deforming means 26, 40 respectively.

Referring now in detail initially to FIGS. 2 and 3 which respectivelyillustrate a vertical sectional view and a plan view of one embodimentof a contact unit, indicated generally by the referance numeral 52, inaccordance with the present invention it may be seen that the contactunit 52 includes a substrate 54 preferably fabricated of a preselectedmetallic material, such as the material comprising the sheet 10described in connection with FIG. 1. A heat sink layer 56 ofa firstpreselected metallic material having a relatively high electrical andthermal conductivity is disposed on one surface of the substrate 54,while a contact layer 58 of a second preselected metallic materialhaving a relatively high electrical conductivity is disposed on anexposed surface of the heatsink layer 56. The heat sink layer 56 and thecontact layer 58 may be affixed in position and deformed into theillustrated configuration generally in accordance with the method asdescribed hereinabove in connection with FIG. I. More particularly, thesubstrate 54 may comprise a suitable low carbon steel, such as describedin connection with FIG. 1, or other metallic material selected with aview to the contemplated usage of the contact unit 52. The substrate 54may be generally coextensive with the overlying heat sink layer 56 ormay be slightly larger, as shown in the illustrated embodiment, in orderto facilitate disposition of the contact unit 52 in position in adesired application. The heat sink layer 56 is preferably fabricated ofa material, such as copper, which is noted for its good electrical andthermal conductivity, and is arranged in a generally circularconfiguration, as particularly illustrated in FIG. 3, while having anonuniform cross-sectional configuration or thickness, including acentral region 560 of a reduced thickness with respect to the peripherythereof. As shown, the contact layer 58 is secured to the exposedsurface of the heat sink layer 56 and preferably comprises a materialhaving a relatively high electrical conductivity and low contactresistance, as well as good corrosion resistance properties, such assilver, gold, palladium, platinum or alloys thereof. In addition, incertain instances a material such as silver cadmium oxide may beutilized in fabricating the contact layer 58. The contact layer 58similarly has a generally circular configuration as shown' in FIG. 3 andis also arranged to have a generally nonuniform cross-section orthickness, including a central region 58a of an increased thickness withrespect to the peripheral portions thereof. The portion 58a of increasedthickness and the portion 56a of decreased thickness of the contactlayer and heat sink layer respectively are disposed in matingrelationship with respect to each other so as to define a structureinwhich an increased amount of contact layer material is provided only atthe central portion of the contact system 52. In addition, as shown, thecontact layer 58 is arranged such that it is noncoextensive with theheat sink layer 56 and terminates at a position spaced inwardly from theperipheral boundary of the heat sink layer. Thus, the total usage of therelatively more expensive contact layer material is minimized, whileproviding an increased amount at the central portion of the contactsystem. Such an ar rang'ement has been found to provid significantbenefits in prolonging the electrical lifetime of the unit, since it hasbeen found that the central region is generally subjected to thegreatest electrical stress, while the relatively larger area, lessexpensive heat sink layer 56 improves the heat dissipation properties ofthe unit 52 so as to permit fabrication of a unit which is lessexpensive but has improved electrical lifetime and current carryingcharacteristics. In this connection a substantial cost and performanceadvantages result from utilizing a system such as that illustrated inwhich more expensive contact material is provided only at the centralregion of the contact unit since such an arrangement minimizes the totalusage of expensive contact layer material by effecting replacement ofsuch material at less critical areas with less expensive heat sinkmaterial. In a preferred embodiment of a unit, such as that illustratedin FIGS. 2 and 3, in which the heat sink layer and contact layer havegenerally circular-shaped peripheral boundaries the contact layer 58occupies between approximately 50 to percent of the exposed surface areaof the heat sink layer. Furthermore, it may be noted that substantialeconomic savings accrue in view of the replacement of more expensivecontact material with less expensive heat sink material since a circulargeometric configuration is involved in which the area varies with thesquare of the diameter.

Although the embodiment illustrated in FIGS. 2 and 3 is shown having acentralregion in which the thickness of the heat sink layer isrelatively abruptly reduced in a stepped configuration to accommodate acorresponding abrupt increase in the thickness of the contact layer, itmay be desirable in certain instances to provide such a system in whicha smooth progressive decrease in thickness in the heat sink layer isaccomplished extending toward the center therof, while the contact layeris arranged to similarly progressively in- .crease in thicknessextending toward the center thereof. Such an embodiment is illustratedin detail in FIGS. 4 and 5. More particularly, in this embodiment asubstrate 60 similar to the substrate 54 is initially provided. A heatsink layer 62 is secured to a surface of the substrate 60, the heat sinklayer including a generally centrally located region 62a of a reducedthickness with respect to the periphery thereof and a contact layer 64is secured to the exposed surface of the heat sink layer 62, the contactlayer having a generally centrally arranged portion 64a of an increasedthickness with respect to the periphery thereof disposed in matingrelationship with the reduced thickness portion 62a. The contact layer640 is noncoextensive with the heat sink layer 62, terminating spacedinwardly from the peripheral boundary of the heat sink layer 62. Theheat sink layer 62 again comprises a material having a relatively goodthermal and electrical conductivity, such as copper, while the contactlayer 64 again comprises a material having a relatively high electricalconductivity, low contact resistance, and good corrosion resistanceproperties such as silver, gold, palladium, platinum or alloys thereofor in certain instances silver cadmium oxide. In this embodiment asshown particularly in FIG. 5 the heat sink layer and contact layer areeach formed in a generally elliptical configuration which has been foundto be advantageous in certain instances. In addition, it may be seenthat the heat sink layer 62 progressively decreases in thickness fromthe outer periphery thereof toward the center while the contact layer 64progressively increases in thickness from the periphery thereof towardthe center thereof so as to define a contact system in which anincreased amount of contact material is provided only at the centerthereof so as to increase the electrical lifetime, while minimizing theusage of relatively expensive contact material. In one example of acontact arrangement such as that illustrated in FIG. 4 it has been foundthat substantial advantages reside in arranging the relative thicknessesof the heat sink layer 62 and contact layer 64 such that there is adifference in relative thicknesses at the respective centers of each ofthese layers of between approximately I to 5 percent, while the outerperipheral edges of each of these respective layers are approximatelyequal in thickness with respect to each other. In addition, it has beenfound particularly advantageous in certain instances to arrange therelative surface dimensions of the heat sink layer and the contact layersuch that the contact layer occupies between approximately to 90 percentof the exposed surface area of the heat sink layer in order to provide astructure in which a substantial cost savings results due to reduced.usage of the relatively expensive contact layer material whileachieving improved electrical lifetime characteristics and currentcarrying abili ties as compared with conventional contact units,utilizing substantially greater quantities of more expensive contactmaterial.

Referring now to FIGS. 6 and 7 another alternate embodiment of thepresent invention is illustrated comprising a contact unit indicatedgenerally by the reference numeral 66 in which an increased volume ofcontact material is provided only at the central region thereof. Moreparticularly, the illustrated embodiment includes a substrate 68 similarto the substrate 60 in the preceding embodiment, as well as a heat sinklayer 70 secured to a surface of the substrate 60 and preferablyfabricated of a material, such as copper having a high electrical andthermal conductivity, and an electrical contack layer 72 secured to aportion of theexposed surface of the heat sink layer 70, the contactlayer 72 being fabricated of a material having a relatively highelectrical conductivity and good corrosion resistance properties, suchas silver, gold, palladium, platinum or alloys thereof or of a materialsuch as silver cadmium oxide. In this embodiment, the heat sink layer 70includes a central region having a plurality of stepped ares 70a and 70bwhich successively decrease in thickness toward the center of the heatsink layer. The areas 70a and 70b are defined by generallycircular-shaped peripheral boundaries, as particularly indicated in FIG.7 so as to define the heat sink layer 70 such that the thickness thereofdecreases progressively towards the center to permit the heat sink layerto accommodate the overlying electrical contact layer 72 which is provided with complementary mating stepped regions 72a, 72b whichsuccessively increase in thickness approaching the center thereof. Moreparticularly, it may be seen that the contact layer 72 similarlyincludes generally circularly bounded stepped areas 72a, 72b whichincrease progressively in thickness toward the center thereof and arearranged in mating relationship with the regions 70a, 70b ofprogressively decreasing thickness of the heat sink layer 70 so as toprovide a central area having a still further increased amount ofcontact layer material at the center thereof while minimizing the actualusage of contact layer material at areas other than the center thereof,thereby providing a completed contact unit in which a maximum volume ofcontact layer material is replaced by less expensive heat sink materialat areas other than the critical central region of the unit so as toprovide a device having improved electrical capabilities in view of theincreased provision of contact layer material at areas of greatest needwhile minimizing the overall usage of contact layer material.

It should be readily apparent that various other alternative shapes ofcontact arrangements maybe readily provided utilizing theabove-described principles in which a central region of a decreasedthickness in the heat sink layer is provided with acorrespondingcomplementary central region of an increased thickness ofcontact layer material being provided in mating relationship therewithso as to define a contact unit in which the usage of relativelyexpensive contact layer material is minimized, while providing a devicehaving requisite electrical lifetime and current carrying capabilities.I

Thus, a novel method has been described for fabricating an improvedelectrical contact unit in which the usage of relatively expensivecontact layer material is minimized, while also eliminating the problemof scrap generation and necessity for recovery thereof. in addition, anumber of contact units which may be fabricated in accordance with theprinciples of such a method have been described in detail.

Various changes and modifications in the above described embodimentswill be readily apparent to those skilled in the art and any of suchchanges or modifications are deemed to be within the spirit and scope ofthe appended claims.

What is claimed is:

l. A method of fabricating an electrical contact device comprisingwelding a first body of a first metallic heat sink material having arelatively high thermal conductivity onto a metal substrate, deformingsubstantially the entire first body into a heat sink layer having aselected shape and a selected peripheral size, welding a second body ofa second metallic material having a high electrical conductivity to acentral portion of said previously formed heat sink layer, and deformingsubstantially the entire second body into an exposed contact layer ofselected peripheral size and shape having the periphery of said contactlayer spaced inwardly from the periphery of said heat sink layer.

2. A method in accordance with claim 1 wherein said first body comprisescopper and said second body is selected from the group consisting ofsilver, silver cadmium oxide, gold, palladium, platinum and alloysthereof.

3. A method in accordance with claim 1 wherein said first and secondbodies are respectively deformed to have generally circular boundedexposed surface portions.

4. A method in accordance with claim 1 wherein said first and secondbodies are respectively deformed to have generally elliptically boundedexposed surface portions.

5. A method in accordance with claim 1 wherein the deformation of saidfirst body to form the central portion of decreased thickness includesdeforming the central portion to include'steppcd regions whichprogressively decrease in thickness toward the center thereof.

6. A method in accordance with claim 5 wherein said first and secondbodies are respectively deformed to have generally circular boundedexposed surface portions and said stepped regions have generallycircularshaped boundaries.

7. A method in accordance with claim 1 wherein said first and secondbodies comprise segments of first and second rod-like members having agenerally circular cross-sectional cofiguration and the diameter of saidsecond rod-like member is approximately between 50 to percent of thediameter of said first rod-like mem ber.

1. A method of fabricating an electrical contact device comprisingwelding a first body of a first metallic heat sink material having arelatively high thermal conductivity onto a metal substrate, deformingsubstantially the entire first body into a heat sink layer having aselected shape and a selected peripheral size, welding a second body ofa second metallic material having a high electrical conductivity to acentral portion of said previously formed heat sink layer, and deformingsubstantially the entire second body into an exposed contact layer ofselected peripheral size and shape having the periphery of said contactlayer spaced inwardly from the periphery of said heat sink layer.
 2. Amethod in accordance with claim 1 wherein said first body comprisescopper and said second body is selected from the group consisting ofsilver, silver cadmium oxide, gold, palladium, platinum and alloysthereof.
 3. A method in accordance with claim 1 wherein said first andsecond bodies are respectively deformed to have generally circularbounded exposed surface portions.
 4. A method in accordance with claim 1wherein said first and second bodies are respectively deformEd to havegenerally elliptically bounded exposed surface portions.
 5. A method inaccordance with claim 1 wherein the deformation of said first body toform the central portion of decreased thickness includes deforming thecentral portion to include stepped regions which progressively decreasein thickness toward the center thereof.
 6. A method in accordance withclaim 5 wherein said first and second bodies are respectively deformedto have generally circular bounded exposed surface portions and saidstepped regions have generally circular-shaped boundaries.
 7. A methodin accordance with claim 1 wherein said first and second bodies comprisesegments of first and second rod-like members having a generallycircular cross-sectional cofiguration and the diameter of said secondrod-like member is approximately between 50 to 90 percent of thediameter of said first rod-like member.